gl_rasterizer_cache: Get rid of variable shadowing

Avoids shadowing the members of the struct itself, which results in a
-Wshadow warning.

src/video_core/renderer_opengl/gl_rasterizer_cache.h

@@ -169,20 +169,28 @@ struct SurfaceParams {
     }
 
     u32 MipBlockDepth(u32 mip_level) const {
-        if (mip_level == 0)
+        if (mip_level == 0) {
             return block_depth;
-        if (is_layered)
+        }
+
+        if (is_layered) {
             return 1;
-        u32 depth = MipDepth(mip_level);
+        }
+
+        const u32 mip_depth = MipDepth(mip_level);
         u32 bd = 32;
-        while (bd > 1 && depth * 2 <= bd) {
+        while (bd > 1 && mip_depth * 2 <= bd) {
             bd >>= 1;
         }
+
         if (bd == 32) {
-            u32 bh = MipBlockHeight(mip_level);
-            if (bh >= 4)
+            const u32 bh = MipBlockHeight(mip_level);
+
+            if (bh >= 4) {
                 return 16;
+            }
         }
+
         return bd;
     }